The present invention concerns the generation of a ramp waveform which is used to drive the vertical deflection coils of a cathode ray tube (CRT) monitor.
A typical prior art circuit which generates a ramp waveform used to drive the vertical deflection coils of a CRT monitor is shown in FIG. 2. A current source 2 charges a capacitor 5. Based on the voltage at the junction of current source 2 and capacitor 5 a power amplifier 4 generates a signal 8 which is connected to the vertical deflection coils. A transistor 9 controlled by an input 3 is used to discharge capacitor 5. The gradual charging of capacitor 5 and the rapid discharge of capacitor 5 by transistor results in signal 8 having a ramp waveform. A variable resistor 7 and a capacitor 6 are shown coupled in series between power amplifier 4 and ground. Capacitor 5, capacitor 6 and variable resistor 7 provide "S" waveform correction for signal 8. This is necessary to take into account the different path lengths of an electron beam in the CRT monitor.
One shortcoming of the circuit in FIG. 2 is that if the frequency of the signal supplied by linear ramp generator varies, this will affect the "S" waveform correction and the magnitude of the ramp waveform of signal 8. Therefore, in order to vary the frequency of the linear ramp generator at order to maintain the same "S" waveform correction and magnitude of the ramp waveform of signal 8.